Portable electronic devices, including cellular phones, personal digital assistants, digital audio players, digital cameras, and the like, increasingly demand higher performance, smaller sizes, and lower power/energy consumption. As a result, circuit components and devices that comprise these portable electronic devices also need higher performance, smaller sizes, and lower power/energy consumption.
One component typically associated with portable electronic devices is a static random access memory (SRAM), which is a memory device that can store or maintain information with little or no power. This type of memory contrasts with dynamic random access memory (DRAM), commonly used in desktop computer systems, that loses stored information without frequent refresh cycles.
Wireless devices can be especially prone to low energy consumption concerns. Many next generation wireless systems employ combined RF-analog-digital systems on a single chip in order to reduce power consumption. Wireless devices, as well as other electronic devices, usually include a suspend/standby mode in which a device is not completely turned off, but is in a “sleep/data retention state” or a low power consumption data retention state. It is important that the memory devices maintain the integrity of stored information during these standby modes.
One problem encountered in SRAM devices is that of leakage during low power or standby/suspend modes. SRAM devices can employ one or more transistors as “voltage keepers” that hold selected control and data access lines (e.g., word line, bit line, and the like) as well as array VSS (VSSA) lines to desired voltage levels during suspend mode, in order to reduce array leakage. However, these voltage keeper transistors themselves can add leakage during suspend mode due to direct gate tunneling leakage of the transistors.